add branch protections for crates-io-auth-action

[marcoieni]

we should also protect the v1 branch, but let's do it in another PR.

Close rust-lang/crates-io-auth-action#2

[github-actions]

Dry-run check results

[WARN  sync_team] sync-team is running in dry mode, no changes will be applied.
[INFO  sync_team] synchronizing github
[INFO  sync_team] 💻 Repo Diffs:
    📝 Editing repo 'rust-lang/crates-io-auth-action':
      Branch Protections:
          main
            Dismiss Stale Reviews: false
            Is admin enforced: true
            Required Approving Review Count: 0
            Requires PR: true
            Required Checks: ["Conclusion"]
            Allowances: []